The present invention generally relates to systems for maintaining aircraft fuel tank ullage in an inert state and more particularly to a hybrid fuel tank inerting system.
Various inerting technologies have been employed to reduce explosion risk by altering the chemical composition of gas vapors in the fuel tanks. Inerting may be achieved by either reducing the oxygen concentration to <12% by volume and/or reducing the fuel to air ratio to <0.03 by weight. Such inerting techniques may include: in-flight purging of fuel vapor from tanks and condensing the purged vapor to reduce the fuel to air ratio; or in-flight generation of inert gas such as nitrogen or CO2 and injection of the inert gas into the fuels tanks to reduce oxygen concentration. Because all of these techniques are performed in-flight, the fuel supply of the aircraft must provide energy to operate the equipment that performs the inerting process. Inerting equipment also adds weight to an aircraft.
As can be seen, there is a need for an inerting system that minimizes aircraft fuel use and adds only minimal weight to an aircraft.